The primary goal of this project is to improve cognitive abilities in patients with Alzheimer's disease. Patients will be chosen from the Massachusetts General Hospital Memory Disorders Unit according to clinical research criteria for Alzheimer's disease. Although patients with Alzheimer's disease as a group have characteristic deficits in cognitive abilities, there are individual variations in the extent to which memory, attention, language, praxis, and visual perception are impaired. New tests will provide information about mechanisms underlying these disorders and reveal the specific aspects of cognition that are improved by treatment. The cholinergic hypothesis of memory dysfunction will be tested by administering combinations of drugs that enhance acetylcholine (ACh) neurotransmission: lecithin plus physostigmine, and lecithin plus piracetam. The double-blind crossover protocols will measure changes in neurological signs, psychiatric state, neuropsychological test performance, and neurotransmitter markers in the cerebrospinal fluid (CSF).